1. Field of the invention
This invention relates to a thermal copying apparatus which makes an original and a plain sheet to be in intimate contact with each other and carries out thermosensitive copying operation by irradiating a light from an exposure source.
2. Description of the prior art
The thermal copying apparatus irradiates an original pressed onto a recording sheet by a light from an exposure source to generate a temperature pattern corresponding to an original image. Due to the temperature pattern, the original image is copied on the recording sheet.
One known example is structured such that a light source is disposed within a transparent tubular member and an original and a recording sheet are fed between the transparent tubular member and a pressure roller which is pressed onto the tubular member.
Another known example is structured such that an original and a recording sheet are pressurized between a flat glass plate and a platen each time they are conveyed by a predetermined distance, and the original is light-radiated through the glass plate.
Those structured as above, however, are disadvantageous in that if foreign matters such as dust in air are entered between the transparent member and the pressure roller or between the glass plate and the platen, then the quality of copying will be outstandingly degraded. Also, the apparatus with the mechanism for intermittently pressurizing the original and the recording sheet will become unavoidably complicated in structure. Further, in multicolor copying operation, the problem of color position deviation would arise from the reciprocal movement of the recording sheet required.
In addition, a temperature bias is caused at the original and the recording sheet due to the temperature of the transparent member, resulting in a change of copying density.
Further in addition, the transparent member will be cooled by the original or recording sheet which are fed, so that the temperature distribution on the surface thereof will be made not-uniform, which will cause an unevenness in copying density.
Still further, the temperature of the transparent member will be increased during copying operation and particularly when it is increased in excess the image copied will become fogged. Thus, the transparent member is required to be cooled. But if it is not uniformly cooled, an evenness in copying density will be caused.